Practice golf ball



Oct. 11, 1949. B. (LEARTON 2,484,397

PRACTICE-GOLF BALL Filed Jan. 30, 1948 A TTIORNEY Patented'oct. 11, 1949PRACTICE GOLF BALL Bernard C. Barton, Clifton, N. J., assignor to UnitedStates Rubber Company, New

York,

N. Y., a corporation of New Jersey Application January 30, 1948, SerialNo. 5,439

4 Claims. (Cl. 273-62) Still another requirement is that they have alonglife and be capable of being struck without showing signs of wear ordisintegrating. In the past practice golf balls have almost invariablybeen made of textile fibers such as yarn. However, such practice golfballs have not been entirely satisfactory for a variety of reasons amongwhich the following may be mentioned. They soon lose their shape. Theirflight is erratic. They are highly absorbent and pick up dirt andmoisture very rapidlv. particularly when they are used out-of-doors.They do not simulate a standard golf ball either in a pearance or inflight.

I have now found that a practice golf ball which is free of the abovedisadvantages of prior art practice golf balls and which has certainexceptional advanta es may be made from closed cell expanded plasticizedpolyvinyl chloride. By making a spherical closed cell ball of expandedplasticized polyvinyl chloride having the dimensions of a standard golfball, there is obtained a practice golf ball which has many advantagesover prior art practice golf balls, particularly over the usual yarnpractice golf ball. If such a closed cell expanded plasticized polyvinylchloride ball be made in such a way that its surface is dimpled or isgiven any uniform pattern of projections or indentations or both such asis conventionally applied to standard golf balls to give them truenessof flight. the resulting practice golf ball strikingly resembles thestandard golf ball and this adds markedly to its appeal.

In the accompanying drawing Fig. l is a front elevation, partially insection, of a dimpled practice golf ball made in accordance with myinvention and Fig. 2 is an enlarged vertical central sectional view of aportion of the practice golf ball illustrated in Fig. 1 and shows inexaggerated detail the closed cell construction of the ball.

The practice golf ball of my invention is characterized by its lightweight, its density generally not exceeding 8 lbs. per cubic ft. andmore commonly being not over lbs. per cubic ft. The density may rangedownwardly from these limits to as low as 3 lbs, per cubic ft. Thepractice golf ball of my invention is particularly characterized by' itslow resilience and its deadness compared with either a closed cellcellular rubber ball or a sponge rubber ball of similar size. Thus inrebound tests carried out under uniform conditions closed cell cellularrubber balls bounced above five to seven times higher than the closedcell polyvinyl chloride ball of my invention. The cellular rubber ballsrebounded from nine to twelve times before coming to rest, whereas mycellular polyvinyl chloride ball rebounded only twice. In the same testthe sponge rubber ball bounced four to five times higher than the ballof my invention, and rebounded nine to thirteen times before coming torest. Low rebound, indicative of deadness, is a highly desirableproperty in a practice golf ball. A swing which would drive a standardgolf ball 250 yards will drive the closed cell polyvinyl chloridepractice ball of the present invention a maximum distance of only about25 yards so that its flight may be readily observed at close range,whereas the same swing will drive the cellular rubber balls from toyards. My improved ball responds in the same manner as a regular golfball to faulty swinging of the club, giving on a smaller scale excellentreproductions of the hook and the slice, whereas a sponge rubber balldoes not show this behavior at all, and cellular rubber balls are toolively to show this behavior at close range. Thus the use of thepractice golf ball of the present invention facilitates practice, makingpossible careful observation of vagaries in the flight of the ballresulting from faulty swinging of the club. It also greatly reduces theamount of walking required to recover the ball, thereby making practiceless tiring and enabling a much greater number of practice strokeswithin a given period of time. The deadness of the ball also permitspractice simulating actual play in areas of restricted size, 0. g., ingymnasiums or in small yards. I

The closed cell expanded polyvinyl chloride practice golf balls of myinvention may be made in a number of ways. One method of producing sucha ball consists of the steps of (1) forming a plastisol, i. e., a pasteof finely divided polyvinyl chloride and a plasticizer therefor which iscapable upon the application of heat of dissolving the polyvinylchloride to form a gel which upon cooling to room temperature will be asolid material capable of retaining its shape, (2) admixing with such aplastisol a chemical blowing agent capable of generating an expandinggas upon the application of heat to the plastisol to gel it, (3) heatingthe plastisol under high presuct wherein the cells do intercommunicate.closed cells of the chemically blown ball of my invention range indiameter from 0.001 to 0.10 inch,

sure in an under-sized mold which conveniently is 7 inch in diameter andthereby effecting simultaneous gelation of the plastisol and generationof the inflating gas by decomposition of ithfl blowing agent, (4)cooling and removing the "miniature molded ball, (5) expanding it in hotwater or in an air oven to approximately regulation golf ball size, 1.e., 1.68 inch, and (6) dimpling the expanded ball by heating it in aregular golf 'ball mold. Alternatively, the dimpling may be accomplishedin the minature mold during step (3) above.

For example, a mixture of powdered polyvinyl chloride, a plasticizer anda blowing agent, in suitable proportions, is formed. A mold having aspherical mold cavity having either smooth walls or walls provided witha suitable design to give a dimpled or similar pattern in miniature tothe pre-molded ball is filled with the resulting mixture. This mold hasa spherical mold cavity which is considerably smaller than the size of astandard golf ball and which conveniently is H inch to inch in diameter.The mold is tightly closed by the application of high pressure, and

;' heat is applied to the mold to cause the blowing agent to decomposeor gasify and to cause the plastisol to gel. A high external pressure ismaintained on the mold in an efiort to hold it closed against theinternal pressure of the generated gas. After the blowing agent hasgasified and the polyvinyl chloride has gelled the mold is cooled, thepressure is released and the miniature ball is removed from the mold. Atthis stage the ball has been only partially expanded and the gas iscontained under pressure in very small pores within the plasticizedresin. The thus prepared ball is then caused to expandfurther to severaltimes its original size to give a very light cellular ball while stillretaining its spherical shape, by

';- heating it, as by placing the ball in warm water or in heated air orin any other heated fluid medium in which it is free to expand so thatthe thermoplastic resin softens and the pressure of the gas causes thepores to become greatly enlarged. Upon cooling the ball retains itsexpanded shape.

It should be noted that the present invention I relates to closed-cellgas-expanded balls, the cells of which do not communicate with oneanother, in contrast to a sponge or open cell type of prod- The theexact diameter depending upon the fineness of comminution of the blowingagent which, it will be understood, is substantially insoluble in theplastisol and is uniformly dispersed in finely -.divided formtherethrough.

The polyvinyl chloride resin used in practicing my invention is awell-known material. I prefer to use polymerized polyvinyl chloridehaving a molecular weight of at least 12,000 as measured by knownmethods and a K value of more than 40 and preferably about 60. (For Kvalue see Fikentscher, Cellulose-chemie 1932, page 58.) Al- 1 mostinvariably the polyvinyl chloride employed bis(p-xenyl)triazene may beused. The proportion of the blowing agent employed may vary dependingupon the density and degree of cellularity desired in the ball and uponthe particular blowing agent used. When the preferred blowing agent,alpha,alpha'-azobisisobutyronitrile, is employed, I generally use from12 to 40 parts thereof per parts by weight of polyvinyl chloride.

Any plasticizer which is capable of dissolving the particles of thepolyvinyl chloride upon heating to form a gel may be employed. Examplesare dioctyl phthalate, tricresyl phosphate, dibutyl phthalate, dicaprylphthalate and other high boiling esters and ethers known to beplasticizers for polyvinyl chloride. Usually from V2 to 2 parts byweight of the plasticizer per one part of the polyvinyl chloride isemployed. More commonly the plasticizer is used in an amount rangingfrom 65 to parts per 100 parts of polyvinyl chloride, but these rangesare not critical for the purposes of my invention.

It is also advantageous to employ in the formulation a small quantity ofa heat or light stabilizer for the polyvinyl chloride, an example beingfrom 2 to 5 parts of calcium stearate per 100 parts of polyvinylchloride.

The time and temperature of the preliminary heating operation will varywith the blowing agent employed. The temperature should be sufficientlyelevated to both decompose the blowing agent and cause the plasticizerto dissolve the resin. When using the preferred blowing agent,alpha,alpha'-azobisisobutyronitrile, the preliminary heating is carriedout at a temperature of from 250 to 350 F. for from 6 to 15 minutes.

While the ball of the present invention usually consists of theplasticized polyvinyl chloride in.

closed cell expanded form, with or without a stabilizer for preventingdecomposition of polyvinyl chloride by heat or light, under somecircumstances it may be desirable to include in the formulation a smallamount of a filler or a pigment provided the type and amount of -suchfiller and pigment is not such as to unduly increase the weight of theball. For example, the density of the ball generally should not be over8 lbs. per cubic ft. for satisfactory results. If any filler or pigmentis used it preferably is white in color in order that the resultingpractice golf ball may still have the white color of a standard golfball.

The ball of my invention has a perfectly spherical shape and does notbecome distorted from blows of the golf club, in marked contrast topractice golf balls made of yarn which never are perfectly round andbecome quite distorted after a few practice drives.

The ball of my invention has a smooth imperforate skin covering itsentire exterior surface. This is the result of the molding operationwhich prevents the formation of ruptured cells at the surface. As aconseduencathe surface of the ball does not readily pick up moisture,dirt or other foreign matter.

The practice golf ball of my invention has substantially the samediameter as a regulation golf ball. At present a regulation golf ball is1.68 inches in diameter. The diameter of the practice golf ball of myinvention may vary some! what from this figure without departing fromthe inventive concept. For example, the diameter of the practice golfball of the present invention may range from 1.6 to 1.75 inches althoughit is preferred that it be as near 1.68 inches as possible in order thatpractice conditions may simulate ac- 75 tual playing conditions asnearly as possible.

In the drawing the golf ball I is shown as a solid mass of closed cellexpanded plasticized polyvinyl chloride. The dimples formed in thesurface of the golf ball are designated by reference numeral 2. Theshowing of Fig. 2 is exaggerated. It will be understood that some of theindividual cells in the ball are so small that they cannot be seen withthe naked eye but only with amagnifying glass. v

Example 1 The following formulation is prepared:

. Parts by weight Polyvinyl chloride 100 Calcium stearate 3 Tricresylphosphate 90 Alpha,alpha'-azobisisobutyronitrile 18 The polyvinylchloride, calcium stearate and alpha, alpha azobisisobutyronitrile aredry mixed whereupon the plasticizer is stirred in.

The mix at this point is still a relatively dry powder. It istransformed into a homogeneous paste or plastisol by passing it three tofive times through a meat chopper. Both halves of a smooth sphericalmold having a cavity inch in diameter are filled with the resultingmixture, a slight excess being added to one mold half to insure acoherent ball being formed when the mold is closed. The filled andclosed mold is then heated eight minutes at a platen temperature of 330F. (90 lbs. steam) at a mold-closing pressure of 3600 p. s. 1.; it isthen cooled seven minutes whereupon it is opened and the ball isremoved. The

ball is noticeably larger than the mold cavity when removed, being aboutinch in diameter. If the ball were removed when warm it would expand sorapidly as to be torn by the edge of the mold cavity. Next the ball isheated in water at 85 C. for 15 minutes which expands it to standardgolf ball size, 1. e., to a diameter of approximately 1.68 inches. Theball is held under the water by a close-mesh wire screen. The expandedball is then dimpled in a pair of golf ball mold cups 1.68 inches indiameter by heating it for 12 minutes at a platen temperature of 230 F.,the hydraulic pressure exerted on the mold cups not exceeding 100 lbs.per ball. High pressure in this dimpling operation can cause defectivedimpling, the ball expanding enough to seal the mold at the joint beforethe air is expelled. The mold is cooled to room temperature beforereleasing the hydraulic pressure.

Example 2 Example 1 is duplicated except that the following formulationis used, and that amold H inch in diameter is employed in the moldingoperation.

Par-ts by weight Polyvinyl chloride 100 Calcium stearate 3 Dioctylphthalate 65 Alpha,alpha'-azobisisobutyronitrlle From the foregoing, itwill be seen that the present invention provides a practice golf ballhaving many advantages. The ball is white and has the appearance of astandard golf ball. Its surface is smooth and non-absorbent. The textureof the surface is deceptively similar to that of a standard golf 'ball.It has a very short flight due to its light weight and its deadness andlow resilience and can be used indoors, if desired, with-out injury tothe ball or to the surroundings. In its flight characteristics itduplicates very closely the behavior of a regular golf ball, ex apt ly.It retains its perfectly round shape indefinitely. Watercannot penetratethe ball so that it retains its lightness even though it is used in wetgrass. In fact, because of the closed cell nature of the ball it floatsindefinitely on the surface of water. Because of the non-absorbentnature of the ball it does not readily pick up dirt and if it shouldhappen to become dirty it can be washed with water without possibilityof penetration into the interior. The ball is economical to manufactureand because of its close simulation of the appearance of a standard golfball it has a strong appeal to golf players.

The term plastisol is used herein with the meaning which has becomewell-established in the art. See for example the article A New Techniquein Coatings," by G. M. Howell and R. W. Quarles appearing in OfficialDigest, published by the Federation of Paint and Varnish ProductionClubs, issue #263, December 1946, which contains a thorough expositionof the nature and properties of plastisols. Reference may also be madeto Modern Plastics Encyclopedia, 1947, vol. 1, pages 140 and 484,published by Plastics Catalogue Corporation, New York, and to BritishPatent No. 500,298 which however effects the gelatinization of theplastisol without the application of pressure.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. As a new article of manufacture, a practice golf ball having auniform structure throughout and comprising a spherical mass composedthroughout of closed-cell expanded plasticized polyvinyl chloride, saidball having substantially the dimensions, shape and appearance of astandard golf ball but being characterized by its light weight, itsdeadness, its short flight, and its ability to substantially duplicateon a small scale the flight characteristics of a regular golf ball.

2. As a new article of manufacture, a practice golf ,ball having auniform structure throughout and comprising a spherical mass composedthroughout of closed-cell expanded plasticized polyvinyl chloride, saidmass comprising a gelatinized mixture of polyvinyl chloride andplasticizer in proportions corresponding to from to 2 parts ofplasticizer per one part of polyvinyl chloride, said ball havingsubstantially the dimensions, shape and appearance of a standard golfball but being characterized by its light weight, its density being notover 8 lbs. per cubic ft., its deadness, its short flight, and itsability to substantially duplicate on a small scale the flightcharacteristics of a regular golf ball.

3. As a new article of manufacture, a practice golf ball having auniform structure throughout and comprising a spherical mass composedthroughout of closed-cell expanded plasticized polyvinyl chloride, saidmass comprising a gelatinized mixture of polyvinyl chloride andplasticizer in proportions corresponding to from 65 to 125 parts ofplasticizer per parts of poly vinyl chloride, said ball havingsubstantially the dimensions, shape and appearance of a standard golfball but being characterized by/ its light weight, its density being notover 8 lbs. per cubic ft., its deadness, its short flight, and itsability to substantially duplicate on a small scale the flightcharacteristics of a regular golf ball.

4. As a new article of manufacture, a practice golf ball having auniform structure throughout 8 flight, and its ability to substantiallyduplicate on a small scale the flight characteristics of a regular golfball.

BERNARD C. BARTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Landreth Nov. 27, 1934 Number

